1. Field of the Invention
The present invention relates to a switching power supply device for supplying a voltage to an electrical apparatus, and more particularly to a technique for automatically recovering the electrical apparatus when a circuit of the electrical apparatus is abnormal.
2. Description of the Related Art
It is general that an electrical apparatus with an AC power supply uses a switching power supply device, the switching power supply device having a switching element and a transformer to perform AC-DC conversion, to supply power to a circuit provided in the electrical apparatus. The switching power supply device is configured with a photocoupler to feed back a voltage deviation from a secondary side circuit to a primary side circuit in order to stabilize an output voltage.
A switching power supply device for supplying power to an integrated circuit provided in an electrical apparatus performs control to stop oscillation of a switching element provided in a primary side circuit when a secondary side output voltage is abnormal, in order to prevent the integrated circuit from being broken. For example, in a technique described in JP-A-10-225112, when an output voltage is excessive, an input terminal of a photocoupler provided for a feedback circuit is grounded to control a primary side oscillation circuit thereby stopping oscillation of the primary side oscillation circuit. After the cause of the excessive voltage is removed, a control signal for restart of the oscillation is transmitted to restart the oscillation.
In addition, in a technique described in JP-A-2000-156972, when a photocoupler provided for a feedback circuit fails to cause an output voltage of a switching power supply device to abnormally increase, an input terminal of the photocoupler provided for the feedback circuit is grounded to stop oscillation of a primary side oscillation circuit in a similar manner to the technique described in JP-A-10-225112. In this case, since the cause is derived from the failure of the circuit part (photocoupler), it is necessary to cut off AC power and repair the circuit part.